Hydrogen storage alloy

ABSTRACT

The present invention relates to Ti—Zr—Mn—Cr based Laves Phase hydrogen storage alloy having high hydrogen storage capacity, and excellent slopping and hysterisis characteristics. In the Ti—Zr—Mn—Cr based Laves Phase hydrogen storage alloy, the hydrogen storage alloy has a composition of (Ti 1−x Zr x ) 1+A Mn 2−y Cr y , and has a non-stoichiometry composition because A is larger than 0.

TECHNICAL FIELD

[0001] The present invention relates to a hydrogen storage alloy whichis applicable to fields of hydrogen storage, heat pumps, andcompressors, and, more particularly, to a Ti—Zr—Mn—Cr group Laves phasehydrogen storage alloy which has a hydrogen storage capacity larger thana related art hydrogen storage alloy, and has excellent slopping, andhysteresis characteristics.

BACKGROUND ART

[0002] It is in general known that AB2 type Laves phase hydrogen storagealloys (A: Zr, Tr, B, V, Cr, Mn), having a larger hydrogen storagecapacity, and a fast hydrogen chemical reaction, are applicable tofields of hydrogen storage, heat pump, and the like. However, scientistsD. O. Northwood et. al. reports in “Storing Hydrogen in AB2 Laves phasetype Compounds” [Z. Phys Chem. N.F., p147, p191-209, 1986] that, as aresult of study of hydrogen reaction behavior of the alloy, though thealloy has excellent in view of a hydrogen storage capacity, and reactionspeed, a resultant hydrogen compound is too stable, with a tendency veryconservative in emigration of hydrogen, to apply to practicalapplications, in which reversible hydrogen emigration is required. Thisis caused by a very low plateau pressure below the atmospheric pressureat a room temperature, and current researches are focused on elevatingthe plateau pressure.

[0003] As one of examples of such researches, Shaltiel et. al. [J.Less-Comm. Metals, p73, p369-376, 1980], Northwood [J. Less-Comm.Metals, p147, p149-159, 1989], et. al. report three element alloy inwhich Ti instead of Zr, and Fe instead of Cr, are substituted, andWallace [U.S. Pat. No. 4,556,551], and Jai-Young Lee [U.S. Pat. No.5,028,389], et. al. report four element alloy. The four element hydrogenstorage alloy reported by Jai-Young Lee [U.S. Pat. No. 5,028,389] isadvantageous in that the plateau pressure can be varied as requiredwithin a range of 0.1-10 atmospheres which is common for many field ofapplications by varying Cr, and Fe contents. However, though the alloy[a four element hydrogen storage alloy having composition ofZr_(1−x)Ti_(x)Cr_(1+y)Fe_(1+y), where 0.05≦x≦0.1, 0≦y≦0.4] disclosed inU.S. Pat. No. 5,028,389 has a hydrogen storage capacity (1.6 wt %)greater than the present alloy (1.3 wt %), the hydrogen storage capacityis still too small. Moreover, the great hysteresis, a pressuredifference between absorption, and discharge of hydrogen, is an obstaclefor putting into commercial use, and developing high performance systemsin the fields of applications due to a great energy loss in theabsorption and discharge of hydrogen.

[0004] Accordingly, there have been many researches for developingalloys having great hydrogen storage capacities, inclusive of Y.Moriwaki et. al. [J. Less-Comm. Metals, p172-174, p1028-1035, 1991]reporting Ti_(1−x)Zr_(x)Mn_(2−y)Cr_(y) alloy, and T. Gamo et. al. [Int.J. Hydrogen Energy, 10(1985) 39] reportingTi_(0.9)Zr_(0.1)Mn_(1.4)Cr_(0.4)V_(0.2) alloy. Though the alloy reportedby prof. Moriwaki, employing Ti as a major element instead of Zr, has agood hydrogen storage capacity of approx. 2 wt % because Ti with anatomic weight approx. 47 g/mol is lighter than Zr with an atomic weightapprox. 91 g/mol, the alloy of prof. Moriwaki has a disadvantage ofsignificant increase of slopping when a Zr content is increased forreduction of the plateau pressure. Therefore, it is very important todevelop an alloy that allows to drop the plateau pressure without changeof hydrogen storage capacity, and still has small hysteresis andslopping.

DISCLOSURE OF THE INVENTION

[0005] Accordingly, the present invention is directed to a hydrogenstorage alloy that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

[0006] An object of the present invention is to provide a hydrogenstorage alloy which has a large hydrogen storage capacity, a low plateaupressure, and small hysteresis and slopping.

[0007] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0008] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, thehydrogen storage alloy of Laves phase in Ti—Zn—Mn—Cr group hascomposition of (Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y), where ‘A’ isgreater than ‘0’, to have non-stoichiometry composition.

[0009] The ‘A’ is preferably in a range greater than ‘0’ and smallerthan approx. 0.2.

[0010] Preferably, the ‘X’ is in a range of 0≦X≦0.3, and ‘Y’ is in arange of 1.0≦Y≦1.2.

[0011] The Cr is preferably substituted with ‘M’ having at least one ofV and Cu, to have composition of(Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y−B)M_(B), wherein the ‘B’ is in arange greater than 0, and smaller than approx. 0.4.

[0012] In other aspect of the present invention, there is provided ahydrogen storage alloy of Laves phase in Ti—Zn—Mn—Cr group wherein theCr is substituted with ‘M’ having at least one of V and Cu, to havestoichiometry composition of Ti_(1−x)Zr_(x)Mn_(2−y)Cr_(y−B)M_(B).

[0013] The ‘B’ is preferably in a range greater than 0, and smaller thanapprox. 0.4.

[0014] Preferably, the ‘X’ is in a range of 0≦X23 0.3, and the ‘Y’ is ina range of 1.0≦Y≦1.2.

[0015] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory, and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciples of the invention:

[0017] In the drawings:

[0018]FIG. 1 illustrates a P-C-T graph comparing a hydrogen storagealloy in accordance with a first preferred embodiment of the presentinvention and a related art hydrogen storage alloy;

[0019]FIG. 2 illustrates a P-C-T graph comparing a hydrogen storagealloy in accordance with a second preferred embodiment of the presentinvention and a related art hydrogen storage alloy;

[0020]FIG. 3 illustrates a P-C-T graph comparing hydrogen storage alloysin accordance with a third preferred embodiment of the present inventionand a related art hydrogen storage alloy;

[0021]FIG. 4 illustrates a P-C-T graph comparing one of hydrogen storagealloys in accordance with a third preferred embodiment of the presentinvention and a related art hydrogen storage alloy;

[0022]FIG. 5 illustrates a graph showing an XRD analysis of the hydrogenstorage alloy of the present invention;

[0023]FIG. 6 illustrates a graph showing a hydrogenation reaction rateof the hydrogen storage alloy of the present invention;

[0024]FIG. 7 illustrates a P-C-T graph of the hydrogen storage alloy ofthe present invention for different non-stoichiometry compositionratios;

[0025]FIG. 8 illustrates a P-C-T graph of the hydrogen storage alloy ofthe present invention varied as some of a Cr content is substituted withother element;

[0026]FIG. 9 illustrates a P-C-T graph of the hydrogen storage alloy ofthe present invention varied as some of a Zr content is substituted withother element; and,

[0027]FIG. 10 illustrates a table showing a comparison of performance ofthe hydrogen storage alloys of the present invention and the relatedart.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings. A hydrogen storage alloy in accordance with afirst preferred embodiment of the present invention will be explained,with reference to FIG. 1.

[0029] The hydrogen storage alloy in accordance with a first preferredembodiment of the present invention is a Ti—Zr—Mn—Cr group Laves phasehydrogen storage alloy with composition of(Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y), where ‘X’ denotes a Ti contentsubstituted with Zr, Y denotes an Mn content substituted with Cr, and‘A’ denotes an extent of deviation of a sum of contents of Ti, and Zrfrom stoichiometry. The hydrogen storage alloy of the present invention,with ‘A’ greater than ‘0’, has non-stoichiometry composition.

[0030] Referring to FIG. 1, it can be noted that the non-stoichiometryhydrogen storage alloy in accordance with a first preferred embodimentof the present invention has a larger hydrogen storage capacity, andsmaller plateau pressure, slopping, and hysteresis in comparison to therelated art stoichiometry hydrogen storage alloyTi_(0.75)Zr_(0.25)Mn_(0.8)Cr_(1.2). It can also be noted that thegreater the ‘A’, i.e., the greater the deviation from stoichiometrycomposition, various characteristics become the better.

[0031] Referring to FIG. 7, it is preferable that ‘A’ is smaller thanapprox. 0.2. When ‘A’ is greater than 0.1, because the plateau pressurebecomes higher, and a section of the plateau pressure becomes smaller,the hydrogen storage alloy shows a slight decreasing tendency ofhydrogen movement which can be used in a reversible reaction. Therefore,it is more preferable that ‘A’ is in a range greater than ‘0’, andsmaller than approx. 0.1.

[0032] A hydrogen storage alloy in accordance with a second preferredembodiment of the present invention will be explained, with reference toFIG. 2.

[0033] The hydrogen storage alloy in accordance with a second preferredembodiment of the present invention is a Ti—Zr—Mn—Cr group Laves phasehydrogen storage alloy with composition of(Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y−B)M_(B), where ‘M’ denotes at leastone of elements of ‘V’, and ‘Cu, and ‘B’ denotes a range of ‘M’ contentsubstituted for ‘Cr’. The hydrogen storage alloy of the presentinvention has ‘A’ equal to 0’, and ‘B’ at least greater than ‘0’. Thatis, the second embodiment hydrogen storage alloy of the presentinvention is of stoichiometry composition, in which Cr is substitutedwith Cu, and/or V.

[0034] Referring to FIG. 2, it can be noted that the Cr substitutionwith Cu, and/or V from the Cr in the related art stoichiometry hydrogenstorage alloy Ti_(0.75)Zr_(0.25)Mn_(0.8)Cr_(1.2) improves variouscharacteristics.

[0035] Next, a hydrogen storage alloy in accordance with a thirdpreferred embodiment of the present invention will be explained, withreference to FIG. 3.

[0036] The hydrogen storage alloy in accordance with a third preferredembodiment of the present invention is a Ti—Zr—Mn—Cr group Laves phasehydrogen storage alloy with composition of(Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y−B)M_(B), where ‘A’, and ‘B’ are atleast greater than ‘0’, respectively. That is, the third embodimenthydrogen storage alloy of the present invention is of non-stoichiometrycomposition, in which Cr is substituted with Cu, and/or V.

[0037] Referring to FIG. 3, it can be noted that, if the Cr issubstituted with Cu and V, for non-stoichiometry composition, theslopping is improved significantly while the hydrogen storage capacityis maintained. It can also be noted that, if the non-stoichiometrycomposition, and Cu, and V are substituted at a time, the samesubstitution effect exhibits.

[0038] The effect of the third embodiment hydrogen storage alloy[(Ti_(0.75)Zr_(0.25))_(1.05)Mn_(0.8)Cr_(1.05)V_(0.05)Cu_(0.1)] of thepresent invention will be explained, with reference to FIGS. 4, 5, and10. FIG. 4 illustrates a P-C-T graph comparing one of hydrogen storagealloys in accordance with a third preferred embodiment of the presentinvention and a related art hydrogen storage alloy reported by Y.Moriwaki [J. Less-Comm: Metals, p172-174, p1028-1035, 1991], wherein itcan be noted that the hydrogen storage alloy of the present inventionhas a very large hydrogen storage capacity of approx. 2 wt %, andstopping and hysteresis better than the related art alloy.

[0039]FIG. 5 illustrates a graph showing an ERD analysis of the hydrogenstorage alloy of the present invention, wherein it can be noted that thehydrogen storage alloy of the present invention maintains the Lavesphase even in a case Cu and V are substituted at a time in anon-stoichiometry composition state.

[0040]FIG. 6 illustrates a graph showing a hydrogenation reaction rateof the hydrogen storage alloy of the present invention, wherein it canbe noted that approx. 90% of hydrogenation reaction is finished withintwo minutes, which is very excellent.

[0041]FIG. 10 illustrates a table showing a comparison of hydrogenstorage capacities, hydrogen absorption/discharge pressures, andslopping and hysteresis characteristics of the hydrogen storage alloy[(Ti_(0.75)Zr_(0.25))_(1.05)Mn_(0.8)Cr_(1.05)V_(0.05)Cu_(0.1)] of thepresent invention, and the hydrogen storage alloy[Ti_(0.7)Zr_(0.3)Mn_(1.2)Cr_(0.8)Ti_(0.7)Zr_(0.3)Mn_(0.8)Cr_(1.2)] ofthe related art reported by Y. Moriwaki et. al. [J. Less-Comm. Metals,p172-174, p1028-1035, 1991], and the hydrogen storage alloy[Ti_(0.9)Zr_(0.1)Cr_(0.6)Fe_(1.4)] of the related art reported byJai-Young Lee [U.S. Pat. No. 5,028,389], et. al., wherein it can benoted that the hydrogen storage alloy of the present invention has avery excellent hydrogen storage capacity as well as very excellentslopping, and hysteresis characteristics in comparison to the relatedart hydrogen storage alloy.

[0042] In the meantime, referring to FIG. 8, Cu substitution more than0.4 shows a reduction of the hydrogen storage capacity. Therefore, it ispreferable that ‘B’ is less than approx. 0.4. Also, there is tendencythat, even if the slopping is improved when ‘B’ is less than 0.3, thehydrogen storage capacity is reduced, and the slopping is increased onthe contrary when ‘B’ is greater than 0.3. Therefore, it is morepreferable that ‘B’ falls on a range greater than ‘0’ and smaller thanapprox. 0.3.

[0043] In the meantime, referring to FIG. 9, it is preferable that ‘X’is in a range of 0≦X≦0.3.

[0044] In summary, the hydrogen storage alloy of the present inventionhas composition of (Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y−B)M_(B), where‘M’ denotes at least one element of V and Cu. Also, it is the mostpreferable that 0≦A≦0.1, 0≦B≦0.3, 0≦X≦0.3, 1.0≦Y≦1.2.

[0045] For reference, a process for preparing the Ti—Zr—Mn—Cr groupLaves phase hydrogen storage alloy of the present invention will beexplained.

[0046] An amount of each of the elements in(Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y−B)M_(B) (‘M’ denotes at least one ofV and Cu) is fixed, to fall atom ratios of element contents withinranges of 0≦A≦0.1, 0≦B≦0.3, 0≦X≦0.3, 1.0≦Y≦1.2, and to amount in a rangeof 5 g in total, which is then subjected to plasma arc melting under anargon atmosphere. In order to enhance a uniformity of a specimen, aprocess of turning over, and re-melting the specimen is repeated for afew times (for an example, 4-5 times) after the specimen is solidified.Then, the melted specimen is crushed, and only specimens with 100-200mesh are put into a Sievert's automatic P-C-T(Pressure-Composition-Temperature) curve measuring equipment, andhydrogenation reaction characteristics is measured. Then, foractivation, an inside of a reaction tube is maintained at approx. 10⁻²Torr for approx. 10 min., heated for approx. 5 min. with an alcohollamp, and cooled down with cold water in a state hydrogen with approx.20 atmospheres is applied. In this instance, a hydrogen reaction iscompleted within approx. 5-10 min., the reaction tube is maintained atvacuum, to release all hydrogen in the specimen, and such a hydrogenabsorption/releasing processes are repeated for a few times (for anexample, 2-3 times) such that the hydrogen absorption/releasingprocesses can be completed within a few minutes. Then, a hydrogenstorage alloy (Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y−B)M_(B) (‘M’ denotesat least one of V and Cu) with ratios of element contents within rangesof 0≦A≦0.1, 0≦B≦0.3, 0≦X≦0.3, 1.0≦Y≦1.2, i.e., a hydrogen storage alloywhich can drop the plateau pressure, and has smaller hysteresis andslopping characteristics, without chance in the hydrogen storagecapacity, can be prepared.

INDUSTRIAL APPLICABILITY

[0047] As has been explained, the hydrogen storage alloy of the presentinvention can improve slopping, and hysteresis characteristicssignificantly while the hydrogen storage capacity is maintained in arange of 1.9 wt %, and the plateau pressure is maintained below 10atmospheres, permitting to provide a system stability, and improve anoutput in application fields of hydrogen storage, heat pump, andcompressor, and the like.

[0048] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the hydrogen storage alloyof the present invention without departing from the spirit or scope ofthe invention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

1. A hydrogen storage alloy of Laves phase in Ti—Zn—Mn—Cr group havingcomposition of (Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y), where ‘A’ isgreater than ‘0’, to have non-stoichiometry composition.
 2. A hydrogenstorage alloy as claimed in claim 1, wherein the ‘A’ is in a rangegreater than ‘0’ and smaller than approx. 0.2.
 3. A hydrogen storagealloy as claimed in claim 2, wherein the ‘A’ is in a range greater than‘0’ and smaller than approx. 0.1.
 4. A hydrogen storage alloy as claimedin claim 3, wherein 0≦X≦0.3, and 1.0≦Y≦1.2.
 5. A hydrogen storage alloyas claimed in one of claims 1-4, wherein the Cr is substituted with ‘M’having at least one of V and Cu, to have composition of(Ti_(1−x)Zr_(x))_(1+A)Mn_(2−y)Cr_(y−B)M_(B).
 6. A hydrogen storage alloyas claimed in one of claims 5, wherein the ‘B’ is in a range greaterthan 0, and smaller than approx. 0.4.
 7. A hydrogen storage alloy asclaimed in one of claims 6, wherein the ‘B’ is in a range greater than0, and smaller than approx. 0.3.
 8. A hydrogen storage alloy of Lavesphase in Ti—Zn—Mn—Cr group wherein the Cr is substituted with ‘M’ havingat least one of V and Cu, to have stoichiometry composition ofTi_(1−x)Zr_(x)Mn_(2−y)Cr_(y−B)M_(B).
 9. A hydrogen storage alloy asclaimed in claim 8, wherein the ‘B’ is in a range greater than 0, andsmaller than approx. 0.4.
 10. A hydrogen storage alloy as claimed inclaim 9, wherein 0≦X≦0.3, and 1.0≦Y≦1.2.